Electronic ignition system for internal combustion engines



ELECTRONIC IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES Filed Dec.

W. A. EARP.

May 30, 1967 3 Sheets-Sheet 1 mo ommwz y lwgmut ENUILLIRH ADAMS A-RP W. A. EARP May 30, 1 967 ELECTRONIC IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES 3 Sheets-Sheet 2 Filed Dec.

haven-r01 5 wlLLlAH ADA-Hi AQP AGGMT May 30, 1967 w. A. EARP ELECTRONIC IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES 5 Sheets-$heet Filed Dec 14, 1964 IML GM f WLUAM mms GAE? Kurd United States Patent ELECTRONIC IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES William Adams Earp, Glenthorne, 34 Chapel Road,

- Pawlett, Bridgwater, England Filed Dec. 14, 1964, Ser. No. 417,879

Claims priority, application Great Britain, Dec. 14, 1963,

7 Claims. (Cl. 123-148) This invention relates to an electronic ignition system for internal combustion engines of the type which includes a contact breaker or other potential changer which operates to render a semi-conductor or other bi-stable state uni-directionally conductive device either conductive or non-conductive, the device controlling the flow of current through the primary winding of an ignition coil and causing this primary current to be interrupted to induce a large electromotive force across the secondary winding of the ignition coil, this high voltage impulse then being distributed to the sparking plugs of the engine.

In the normal form of ignition system fitted to the majority of internal combustion engines there has been provided a contact breaker and ignition coil with a capacitor connected in parallel across the breaker points of the contact breaker. In this conventional type of ignition system a rotating cam driven from the cam shaft or crank shaft of the engine causes the breaker points to open at a pre-determined time to interrupt the flow of current in the primary winding of the ignition coil thereby inducing a large voltage impulse across the secondary winding of the coil.

The period of growth of the current in the primary winding is extended due to the opposing voltage set up in the primary winding when the breaker points close but when the breaker points open the induced primary voltage tends to maintain the existing flow of primary current which would continue to flow across the contact breaker gap in the form of an arc, were it not prevented from doing so by the action of the capacitor. When the primary circuit is interrupted by the opening of the breaker points a high voltage impulse is induced in the secondary winding and successive impulses are distributed in predetermined sequence to the sparking plugs of the engine to produce the necessary sparks.

A major disadvantage of this conventional type of ignition system is the comparatively long period of time required to fully magnetise the core of :the ignition coil and it will be appreciated that as the speed of the engine revolutions increases then the time for which the contact breaker points are closed is diminished until eventually an engine speed is reached when the breaker points have to open before the core is fully magnetised. The result of such a situation is the production of a much weaker spark which is sometimes inadequate to ignite the fuel thereby causing mis-firing and imposing a limitation upon the maximum speed of the engine.

Attempts have been made to overcome the aforementioned disadvantages by the introduction of a semiconductor device into the ignition system. In such an electronic ignition system the number of turns of the primary winding of the ignition coil has been reduced whilst the current through it has been increased, thereby maintaining or improving the strength of the magnetic field since this is proportional to the product of the number of turns on the primary winding and the current flowing through it.

Since the time taken to magnetise the core of the ignition coil to its maximum practical value is also a function of the number of turns in the primary winding a more rapid magnetisation of the core has been possible thereby enabling higher engine speeds to be obtained.

A further advantage of such an ignition system is that only a very small current need pass across the contact breaker points, thereby reducing the wear and tear upon the points themselves. The semi-conductor device can quite easily pass the large currents flowing in the primary circuit so that the contact breaker then only acts as a trigger to render the semi-conductor device either conductive or non-conductive.

The semi-conductor device utilised in such electronic ignition systems has usually been a transistor of the N-P-N type wherein a negative potential applied to the base electrode of the transistor cuts off the current flow through the collector and emitter electrodes. Thus, a circuit may be built up in which only a small trigger current controlled by the contact breaker serves to effectively switch on or switch off the flow of current through the transistor. Although a N-P-N type of transistor has usually been utilised it would of course be possible to utilise a P-N-P type wherein the application of a negative potential to its base electrode causes the transistor to become conductive.

Some examples of such use of transistors are illustrated in FIGURES 1 to 4 of the drawings wherein:

FIGURE 1 is a circuit diagram of an ignition system utilising an N-P-N transistor in association with an ignition coil of which the primary winding is not directly earthed.

FIGURE 2 is a circuit diagram of a modified system still using an N-P-N transistor and functioning generally similarly to that of FIGURE 1, but with the primary winding of the ignition coil earthed.

FIGURE 3 is a circuit diagram differing from that of FIGURE 1 in the utilisation of a P-N-P transistor, and

FIGURE 4 is a circuit diagram diflering from that of FIGURE 2 in the utilisation of a P-N-P transistor.

However, in such system as illustrated in the ,above mentioned figures, the basic disadvantage still exists that time is wasted whilst the collapsed magnetic field is built up again ready for the next induced spark, and it has been found that this wasted time amounts to a minimum of approximately 33% of the time between consecutive induced im-pulses from the secondary winding. It is the object of the present invention to provide an improved form of electronic ignition system which will overcome this inherent disadvantage and give a large increase in efficiency and maximum engine speed.

According to the broadest aspect of the present invention I provide an ignition system for an internal com-busti-on engine, in which switching means for controlling the flow of current in the primary winding of an ignition coil comprises two or more bi-stable state uni-directionally conductive devices included in the primary circuit, a sequentially operable potential changer for applying controlling potentials to the devices to render each of them alternately conductive and non-conductive, and at least one of the two devices providing when conductive a path for the flow of current from a uni-directional current source through at least part of the primary winding of the ignition coil in a direction opposite to that determined in at least part of the primary winding by the same device being non-conductive, whereby the magnetic field generated by the primary winding is reversible by each successive operation of the potential changer.

By a bi-stable state uni-directionally conductive device is meant a device of the kind which is selectively re sponsive to controlling potentials to change its state, beingconductive of current in only one direction in one state and'non-conductive of current in any direction in the other state. Typical examples of such devices are semiconductor devices, for instance transistors and semi-conductor controlled rectifiers.

Preferably, but not necessarily, there will be two bi stable state uni-directionally conductive devices, and each when conductive will provide a path for the flow of current through at least part of the primary winding in a direction opposite to that at least in part determined in at least part of the primary winding 'by the same device being non-conductive.

The arrangement may be such that each of the devices is adapted to be rendered, by the potential changer, alternately conductive and non-conductive in reverse to the other, and each device providing when conductive a path for the flow of current in the primary winding in the opposite direction to that provided in the winding by the other device when conductive.

In this case the devices may be complementary, that is one of them being responsive to a change of controlling potential in one sense to change its state in one direction and the other being responsive to a change of controlling potential in that one sense to change its state in the ther direction. In this aspect of the invention the primary winding may be tapped intermedia-tely of its ends, one of the devices controlling the current flow in one direction between the tapping and one end of the winding and the other device in the opposite direction between the tapping and the other end of the winding.

Where there are specifically two of the bi-stable devices, they may be separately included in two sides of a four-sided network, with the primary winding connected across two opposite corners of the network and provision for connecting the source of uni-directional current to the other corners of the network, the effect of the potential changer being to reverse the voltage across the primary winding. In one modification of this arrangement two further bi-stable state uni-directionally conductive devices may be included in the remaining sides of the bridge, in which case the devices in two opposite sides of the network may be complementary to the devices in the other two sides of the network.

Alternatively two complementary devices may be in cluded in adjacent sides of the network with the primary winding connected across the outer ends of these sides; or the two devices may be non-complementary and included in opposite sides of the network.

Preferably the bi-stable state uni-directionally conductive devices will be transistors. An N-P-N type transistor and a P-N-P type transistor are typically complementary transistors; on the other hand two transistors of the N-P-N type are non-complementary, as are two transistors of the P-N-P type. The meaning of the terms complementary and non-complementary as used herein particularly illustrated in the case of transistors wherein the application of a negative potential to the base electrode relative to the emitter electrode causes the N-P-N type to become non-conductive and the P-N-P type to become conductive.

Some electronic ignition systems constructed in accordance with the invention will be described hereinafter in more detail by way of example with reference to FIG- URES 5 to of the accompanying drawings wherein:

FIGURE 5 is a circuit diagram of an ignition system utilising complementary N-P-N and P-N-P transistors;

FIGURE 6 is a circuit diagram functioning similarly to that shown in FIGURE 5 but wherein the primary winding of the ignition coil is at earth potential;

FIGURE 7 is a circuit diagram representing another manner of utilising complemetary transistors in a 4- sided network;

FIGURE 8 is a modification of the arrangement shown in FIGURE 7;

FIGURE 9 is a circuit diagram representing the use of two non-complementary transistors in a 4-sided network; and

FIGURE 10 represents yet another arrangement using two non-complementary transistors.

Referring first to the previous proposals for using transistors, in FIGURE 1 there is shown a primary circuit comprising a battery B with its positive terminal earthed and its negative terminal connected through an ignition switch IS and a ballast resistor RB to one end of the primary swinding P of an ignition coil, the other end of which is connected through a capacitor C to the earthed positive battery terminal. The contact breaker points CB are connected between the positive battery terminal and one resistor R2 of a potential divider comprising two resistors R1 and R2 of which the other end is connected between the ignition switch IS and the ballast resistor RE. The tapping point of the potential divider is connected to the base electrode b of the N-P-N type transistor T1. The collector and emitter electrodes 0 and B respectively of the transistor T1 are connected to opposite sides of the capacitor C such that e is negative and C is positive. One end of the secondary winding S of the ignition coil is connected to, so as to be at the same potential as, the said other end of the primary winding P.

In operation, a cam driven from the cam shaft or crank shaft of the engine causes the contact breaker points CB to open and close and in this circuit, with the ignition 1S closed, when the cam opens the breaker points CB the potential on the base electrode b of the transistor T1 is negatively driven to cut off the flow of current through the transistor and hence through the primary winding P of the ignition coil. This interruption of the current flow through the primary winding causes a rapid collapse of the magnetic field thereby inducing a high voltage across the secondary winding which is then sequentially distributed to the sparking plugs. The capacitor C will serve to absorb any surge due to bZICK-E-MJF. from the primary winding P, which otherwise might damage the transistor.

When the cam next allows the breaker points CB to close, the potential of the base electrode b of the transistor T1 is positively driven thereby effectively switching on the transistor so that it passes current through the primary winding P and re-magnetises the core of the ignition coil. From such a circuit it will be seen that certain advantages are gained in as much that there is no necessity for the provision of a condenser across the contact breaker points and only a very small current actually passes across these points.

FIGURE 2 differs from FIGURE 1 in that the capacitor C and its connections with the collector and emitter electrodes 0 and e are connected between the ballast resistor and the junction between the potential divider and the ignition switch. It has been found that this is a preferable method of arranging this type of ignition circuit, the common junction between the primary and secondary windings of the ignition coil operating at earth potential.

FIGURE 3 is a circuit arrangement which differs from that shown in FIGURE 1 in that a P-N-P type transistor T2 is utilised. When the cam causes the breaker points CB to open the potential of the base electrode of the transistor T2 is negatively driven as before, but since transistor T2 is a P-N-P type it behaves in the opposite manner to the transistor T1 and effectively switches on to allow current to flow through the primary winding P of the ignition coil. Conversely, when the cam allows the contact breaker points CB to close, the potential of the base electrode b is positively driven thereby stopping the flow of current through the transistor T2 and hence through the primary winding P and thereby inducing the required high voltage across the secondary winding S.

FIGURE 4 differs from FIGURE 2 by the use of the P-N-P type transistor T2 instead of the N-P-N type transistor T1; in operation it is the equivalent of the circuit shown in FIGURE 3 but with the ignition coil operating at earth potential.

Thus in all of the arrangements shown in FIGURES 1 to 4 the required induced voltage across the secondary winding of the ignition coil is produced upon either the opening or the closing of the contact breaker points CB. Utilising the N-P-N type of transistor T1 as shown in FIGURES 1 and 2, the induced voltage is produced upon opening of the contact breaker points CB and the period when the points are closed is utilised to re-magnetise the core of the ignition coil whilst the converse effect is obtained when the P-N-P type of transistor T2 is utilised as shown in FIGURES 3 and 4.

In the arrangement in accordance with the invention, shown in FIGURE 5 the connection from the negative terminal of the battery B is taken through the ignition switch IS and ballast resistance RB to a centre or near centre tapping of the primary winding P of the ignition coil. One end of the secondary winding is connected to the positive battery terminal.

The two ends of the primary winding P are connected to the positive battery terminal through transistors T1 and T2 respectively, the transistors being complementary; transistor T1 is of the NP-N type and transistor T2 is of the P-N-P type. The control of the potentials on their base electrodes is provided by the contact breaker points CB connected between the earthed positive battery terminal and the potential divider comprising the resistors R1, R2 and R3, the common junction of resistors R2 and R3 being connected to the contact breaker CB, their other ends being connected respectively to the base electrodes of transistors T1 and T2, and resistor R1 being connected between the base electrode of transistor T1 and the junction between the ballast resistor RB and the ignition switch IS.

When the breaker points CB are open a negative potential is applied to the base electrodes of the transistors T1 and T2 and thus allowing a current to flow through the P-N-P type transistor T2 in one direction in one part of the primary winding P and preventing current from tflowingthrough the N-P-N type transistor T1. Conversely, when the contact breaker points close a less negative potential is applied to the base electrodes thus rendering the N-P-N type transistor T1 conductive, so that current flows in the opposite direction in the other part of the primary winding P, and the P-N-P type transistor T2 nonconductive. Thus by providing for the contact breaker CB to control both of the complementary transistors T1 and T2, a flow of current is always present Within the primary winding P of the ignition coil but will change its direction every time the breaker points open or close. By this arrangement the core of the ignition coil is rernagnetised to its maximum practical value at both the opening and the closing of the contact breaker points and the magnetic field so produced is of opposite polarity at the opening of the breaker points to that at the closing. The collapsing magnetic field at each change over of direction of flow of current in the primary winding is thereby assisted by this reversal of the current flow and a more rapid collapse of the magnetic field is thus provided so that a larger high voltage is induced in the secondary winding S of the ignition coil at both the opening and closing of the contact breaker points.

Since the magnetic field in the core of the ignition coil is effectively driven to collapse each time that the core is in the process of being re-magnetised in the reverse direction, the voltage output from the secondary winding is effectively doubled thereby producing a much larger spark than that obtainable with the prior arrrangements, and the maximum engine speed can be thereby effectively doubled over that obtainable with the circuits shown in FIGURES l to 4.

The essential difference between the arrangements shown in FIGURES 5 and 6 is that in the latter figure the complementary transistors T1 and T2 are connected between the ends of the intermediately tapped primary winding P and the ballast resistor RB. The tapping on the primary winding P and the one end of the secondary winding S are each connected to the earthed positive battery terminal. The resistor R1 of the potential divider is connected between the base electrode of the N-P-N type resistor T1 and the junction between the ballast resistor RB and the ignition switch IS. The remaining resistors R2 and R3 are connected in series between the base electrodes of the transistors T1 and T2 and their common junction is connected through the contact breaker CB with the positive battery terminal. The transistor T1 is connected between one end of the primary winding P and the ballast resistor RB, and the other, the P-N-P type, transistor T2 is connected between the other end of the primary winding P and the ballast resistor RB. As in the arrangement of FIGURE 5, current flows in one direction in the primary winding when the contact breaker opens and in the opposite direction when the contact breaker closes, thus providing the same adv-antageous results as are referred to above in connection with FIGURE 5.

FIGURE 7 illustrates an arrangement in which the sequential reversal of current occurs throughout the full length of the primary winding P. As in FIGURES 5 and 6 there are provided complementary transistors, namely a P-N-P type transistor T2 and and N-P-N'type transistor T1 which are series connected in one branch of a bridge network of which the other parallel branch comprises two series connected ballast resistors RBl and RB2. The primary Winding P is connected to the common junctions of the ends of those branches of the network. The negative battery terminal is connected to the junction between the ballast resistors RBI and RB2, and the positive battery terminal, which is earthed, is connected to the junction between the transistors T1 and T2. A potential divider comprises four resistors R1, R2, R3 and R4 connected in that order in series across the battery, such that the outer end of the resistor R1 is connected to the negative terminal and the outer end of resistor R4 is connected to the positive terminal. The junction between resistors R1 and R2 is connected to the base electrode of the N-P-N type transistor T1 and the junction between resistors R3 and R4 is connected to the base electrode of the other, P-N-P type transistor T2. The contact breaker CB is connected across resistors R3 and R4, while the ignition switch IS is connected between the negative battery terminal and what is in effect a common connection between the outer end of resistor R1 and the junction between the ballast resistors RBI and RB2. By appropriately selecting the relative values of the parts of the potential divider it is arranged that with the contact breaker CB open the base electrodes are negatively driven so that transistor T2 becomes conductive and transistor T1 becomes non-conductive. With the contact breaker closed, the base electrodes are less negatively driven so that the conditions of the transistors are reversed, namely, T2 becomes non-conductive and T1 becomes conductive. When transistor T2 is conductive there is How of current from the positive battery terminal through T2, in one direction through the primary winding P and through ballast resistor RBI to the negative battery terminal. It Will be noticed that there is also an alternative current path through the other ballast resistor RB2 to the negative battery terminal. When the conditions of the transistors are reversed, the energizing current flows through the other transistor T1, in the opposite direction through the primary winding P and ballast resistor R132 to the negative battery terminal; in this case the alternative current path is through ballast resistor RBI. There is thus a reversal of the energizing current through the full length of the primary winding P with each opening and closing operation of the contact breaker CB, so that a high voltage impulse will be induced in the secondary winding S and there will he a minimum lapse of time required for building up the magnetic field in the core of the induction coil between successive high voltage pulses as before.

In the last mentioned arrangement the flow of current in the so-called alternative paths through each of the ballast resistors in turn represents a certain loss of energy,

but this loss is, in relation to previously proposed arrangements, more than compensated by the increased efficiency of the arrangements for controlling the production of the required high voltage in the secondary winding. However even that loss of energy may be reduced or even eliminated by the modification represented in FIGURE 8.

In FIGURE 8 the previously provided ballast resistors RB1 and RB2 of FIGURE 7 are replaced by transistors T3 and T4 respectively, the first being of the P-N-P type and the second of the N-P-N type. The base electrode of the P-N-P type transistor T3 is connected to the same point on the potential divider as is the base electrode of the N-P-N type transistor T1, so that when one of them is conductive the other will be nonconductive. The base electrodes of the complementary transistors T4 and T2 are connected to points on the potential divider so that the conditions of one will aways be the reverse of that of the othenOtherwise the circuit of FIGURE 8 is similar to that of FIGURE 7. As in FIGURE 7, when transistor T1 is conductive, transistor T2 being non-conductive, there is a flow of current in one direction through the primary winding P and transistor T4 which is conductive at the same time as transistor T1; at this time however, transistor T3 is non-conductive so that the alternative current path, previously provided by ballast resistor RB1 is blocked. In the other condition, the reverse current in the primary winding P flows through the conductive transistors T2 and T3, the alternative current path being blocked by transistor T4 replacing the ballast resistor RB2 and being non-conductive in this condition of the circuit.

In the arrangements illustrated in FIGURES 7 and 8 the one end of the secondary winding S is connected to the earthed positive battery terminal and is not connected to the primary winding P. Since in this arrangement the primary winding P is not tapped, the induction coil may be a standard form in which, for other reasons, there is no common connection between the two windings.

The bridge arrangement shown in FIGURE 7 represented a 4-sided network with complementary transistors included one in each of two adjacent sides with the primary winding connected across the outer ends of those sides.

In FIGURE 9 is shown an arrangement in which noncomplementary transistors T1, T2, each being of the N-P-N type are connected in opposite sides of a 4-sided network. In this case the negative battery terminal is earthed and the potential divider of four resistors R1, R2, R3, R4 in series is connected across the battery with resistor R1 at the positive end. The contact breaker CB is connected between the negative battery terminal and the common junction between resistors R2, R3. From the positive battery terminal there is a connection through a limiting resistor RL1 into one junction of the network, and the opposite junction is connected through a limiting resistor RL2. to the earthed negative battery terminal. From the first mentioned junction, one branch of the network comprises a ballast resistor RB1 connected to the collector of transistor T1 of which the emitter is connected to the other junction. In the other branch there is an opposite arrangement of a transistor T2 and ballast resistor RB2, the collector of T2 being connected to the first limiting resistor RL1 and its emitter being connected to the ballast resistor RB2. The primary winding P is connected from the junction of resistor RBI and the collector of transistor T1 to the junction of the emitter of transistor T2 and resistor RB2. The base of transistor T1 is connected to the junction of resistors R3, R4; and the base of transistor T2 is connected to the junction of resistors R1, R2. One end of the secondary winding S is connected to the earthed negative battery terminal. As in previous arrangements the transistors T1, T2 are provided with shunt capacitors C1, C2 respectively.

It will be apparent from the circuit that when the contact breaker CB is closed, the transistors are non-conductive and current will flow in one direction from the positive to the negative terminal in the circuits RL1, RB1, P, RB2, RL2. When the contact breaker is open, the transistors will be conductive and there will be a circuit for current flow from the positive to the negative terminal in the sequences RL1, T2, P, T1, RL2. In the second case the direction of flow of current in the primary winding P is opposite to that of the first case. It will also be apparent that the first mentioned circuit through the primary winding is still complete in the second case. However by appropriately selecting the parameters of the circuit it can be determined that the voltage across the primary winding P in one case exceeds the voltage in the opposite sense across it in the other case so that the overall result will be to reverse the primary current at each successive operation of the contact breaker. It will also be seen that when the transistors are conductive there will also be current flowing in paths not including the primary winding, namely through the ballast resistors RB1 and RB2; however, as indicated above, this does not substantially reduce the relative efficiency of the system.

In FIGURE 10 the arrangement comprises a foursided network in which two non-complementary transistors T1 and T2, both of the P-N-P type are included one in each of two adjacent sides of a four-sided network. One branch comprises the transistors arranged back-to-back, their collectors being at the two ends of the branch, and their emitters being connected through series limiting resistors RL1, RL2. The other branch, that is the other two adjacent sides, of the network comprises the series ballast resistors RB1 and RB2. The primary winding P is connected across the junctions of the two branches. The common junction of the ballast resis tors RB1, RB2 is connected to the earthed negative battery terminal, to which one end of the secondary winding S is also connected, and the positive terminal is connected through the ignition switch IS to the common junction of the limiting resistors RL1 and RL2. The potential changer is somewhat different from those previously described; the contact breaker CB is connected from the negative terminal to the input of a bi-stable state flip-flop or similar known controlled oscillator F, and the output from the oscillator is divided to provide one connection to the base of transistor T1 and another to the base of transistor T2. The arrangement is such that at one state of the oscillator F one transistor will be conductive and the other non-conductive, and at the change of state of the oscillator F those conditions will be reversed. It will be seen from the circuit that the changes of state of the oscillator can be effected by successive operations of the contact breaker CB, current flowing in one direction through the primary P in one state and in the opposite direction in the other state.

In previously known ignition arrangements utilising a single set of contact breaker points the cam which opens and closes the contact breaker points usually has a number of cam projections corresponding to the number of cylinders in the engine. However, by the arrangement according to the invention the number of cam projections can be halved while maintaining the same relation between its speed of rotation and the engine speed. Alternatively, the same number of cam projections as cylinders may still be provided whilst the cam is adapted for rotating at half its normal speed. In yet another arrangement, with a cam having half the number of projections, as compared with the number of cylinders, there may be two contact breaker sets appropriately angularly displaced, as for instance at 45 in the case of a 4-1obe cam in association with the so-called V-8 engine.

Within the scope of the invention are a variety of modifications in the circuits which have been described by way of example. For example the shunt capacitors for the transistors, for instance the capacitors C1 and C2 shown in FIGURES 5 and 6, may be replaced by unidirectional diode devices, such as Zener diodes, and any suitable semi-conductor or other devices as herein defined may be utilised in place of the N-P-N and P-N-P transistors, with the appropriate triggering arrangements.

In the described examples the circuit breaker has been considered to be of the mechanical type wherein a rotating cam causes contact breaker points to open and close to govern the control potential which is applied to the semiconductor devices. However, as an alternative the potential changer may be a rotary induction generator of cyclically variable potential adapted to be driven by the internal combustion engine. Such a' generator may, for instance, comprise one or more permanent magnets or electromagnets which are rotatable past stationary coils, or coils rotatable past stationary permanent magnets or electromagnets, to induce a potential across the coils and this'potential may then be applied as the control potential to the semi-conductor devices, which need not necessarily be of complementary type. Such rotatable magnets or coils may be mounted upon a rotatable drive from the cam shaft or crank shaft of the engine or alternatively they may be mounted directly at some convenient position upon the crank shaft itself, for example, around the periphery of the flywheel.

It will be noted that the reversal of the direction of the generated magnetic field at successive high voltage pulse generating operations gives rise to alternate negative and positive going pulses, simulating to a certain degree the conditions obtained with magneto ignition systems. It is generally recognised that, all other conditions being equal, a higher spark'voltage is desirable for a positive going impulse than for a negative going impulse. By the present invention this condition may be met with the tapped primary winding by offsetting the tapping point from the mid-position to give an appropriate ratio between the two parts of the winding. Where the current is reversed in the Whole length of the primary winding, then an appropriate difference between successive outgoing pulses, could be obtained by arranging for additional loading of the input circuit to the primary winding when the current flows in one selected direction, for example, by making the ballast resistors unequal (FIG. 7) or by shunting the coil primary with a series circuit consisting of a resistor and semi-conductor (FIGS. 7 and 8) or by building a special arrangement into the circuit (FIG. 8).

What I claim then is:

1. In an ignition system for an internal combustion engine, an ignition coil having a primary winding and a secondary winding, a source of uni-directional current, a first supply circuit connecting the primary winding to the source to provide for current flow in one direction in the primary winding, a second supply circuit connecting the primary winding to the source to provide for current flow in the opposite direction in the primary winding, an NPN transistor in the first supply circuit and a PNP transistor in the second supply circuit, a two-state bias-potential controlling circuit interconnecting the source and the transistors, and a two-state switch connected to the controlling circuit to change the state of the controlling circuit at each change of state of the switch, the switch being closed in one state and open in the other state, the NPN transistor being in conductive condition and the PNP tran sistor being in non-conductive condition in one state of the controlling circuit and those conditions of the transistors being reversed in the other state of the controlling circuit, whereby in the primary winding the direction of current flow from the source is reversible by each change of state of the switch.

2. In an ignition system for an internal combustion engine, an ignition coil having a centre tapped primary winding and a secondary winding, a first supply circuit connecting one half of the primary winding onone side of the centre tapping to the source to provide for current flow in one direction in said one half, a second supply circuit connecting the other half of the primary winding on the other side of the centre tapping to the source to provide for current flow in the opposite direction in said other half, an NPN transistor in the first supply circuit and a PNP transistor in the other supply circuit, a two-state bias-potential controlling circuit interconnecting the source and the transistors, and a two-state switch connected to the controlling circuit to change the state of the controlling circuit at each change of state of the switch, the switch being open in one state and closed in the other circuit state, the NPN transistor being in non-conductive condition and the PNP transistor being in conductive condition in one state of the controlling circuit and those conditions of the transistors being reversed in the other state of the controlling circuit, whereby in the primary winding the direction of current flow from the the source is reversible by each change of state of the switch.

3. In an ignition system for an internal combustion engine, an ignition coil having a primary winding and a secondary winding, a source of uni-directional current, a foursided bridge network including resistance in adjacent first and second sides of the network, a PNP transistor in the third side and an NPN transistor in the fourth side of the network, the source being connected across two opposite corners of the network and the primary winding being connected across the remaining opposite corners of the network, a twostate bias-potential controlling circuit interconnecting the source and the transistors, and two-state switch connected to the controlling circuit to change the state of the controlling circuit at each change of state of the switch, the switch being open in one state and closed in the other state, the NPN transistor being in non-conductive condition and the PNP transistor being in conductive condition in one state of the controlling circuit to complete a path for the flow of current from the source in one direction in the primary winding, and those conditions beingreversed in the other state of the controlling circuit to complete a path for the flow of current from the source in the opposite direction in the primary winding, whereby in the primary winding the direction of current flow from the source is reversible by each change of state of the switch.

4. In an ignition system for an internal combustion engine, an ignition coil having a primary winding and a secondary winding, a source of uni-directional current, a foursided bridge network including an NPN transistor in each of two opposite sides and a PNP transistor in each of the other opposite sides, the source being connected across two opposite corners of the network and the primary winding being connected across the remaining opposite corners of the network, a two-state bias-potential controlling circuit interconnecting the source and the transistors, and a twostate switch connected to the controlling circuit to change the state of the controlling circuit at each change of state of the switch, the switch being open in one state and closed in the other state, the NPN transistors being in non-conductive condition and the PNP transistors being in conductive condition in one state of the controlling circuit to complete a path for the flow of current from the source in one direction in the primary winding and those conditions being reversed in the other state of the controlling circuit to complete a path for the flow current from the source in the opposite direction in the primary winding, whereby in the primary winding the direction of current flow from the source is reversible by each change of state of the switch.

5. In an ignition system for an internal combustion engine, an ignition coil having a primary winding and a secondary winding, a source of uni-directional current, a foursided bridge network having resistors in two adjacent sides and having two similar transistors one in each of the remaining sides of the network, the source being connected across two opposite corners of the network and the primary winding being connected across the other corners of the network, a two-state bias-potential controlling circuit interconnecting the source and the transistors, and a two-state switch connected to the controlling circuit for changing the state of the controlling circuit at each change of state of the switch, the switch being open in one state and closed in the other state, one transistor being in nonconductive condition and the other transistor being in conductive condition in one state of the controlling circuit to complete a circuit through a resistor in one of said adjacent sides of the network and the primary winding for current flow in one direction in the primary winding from the source, and said other transistor being in non-conductive condition and said one transistor being in conductive condition in the other state of the controlling circuit to complete a circuit through a resistor in the other of said adjacent sides of the network and the primary winding for current flow in the opposite direction in the primary winding from the source, whereby in the primary winding the direction of current flow from the source is reversible by each change of state of the switch.

6. In an ignition system for an internal combustion engine, an ignition coil having a primary winding and a secondary winding, a source of uni-directional current, a four-sided bridge network having resistors in two opposite sides thereof, and two similar transistors one in each of the two opposite sides, the source being connected across two opposite corners of the bridge network and the primary winding being connected across the other opposite corners of the bridge network, a two-state bias-potential controlling circuit interconnecting the source and the transistors, and a two-state switch connected to the controlling circuit to change the state of the controlling circuit at each change of state of the switch, the switch being open in one state and closed in the other state, the transistors being in conductive condition in one state of the controlling circuit and in non-conductive condition in the other state of the controlling circuit, the resistors in said two opposite sides of the network providing a first circuit for current flow from the source in one direction in the primary winding and the transistors when conductive providing a second lower resistance circuit for current flow from the source in the opposite direction in the primary winding, whereby in the primary windingthe direction of current flow from the source is reversible by each change of state of the switch.

7. In an ignition system for an internal combustion engine, an ignition coil having a primary winding and a secondary winding, a source of uni-directional current, a first supply circuit connecting the primary winding to the source to provide a path for current flow from the current source in one direction in the primary winding, a second supply circuit connecting the primary winding to the source to provide a path for current flow from the source in the opposite direction in the primary winding, two transistors in the supply circuits, a two-state bias-potential controlling circuit for controlling the transistors, each transistor being changed from a conductive condition to a non-conductive condition by a change of state of the controlling circuit and from a non-conductive condition to a conductive condition by a succeeding change of state of the controlling circuit, the first supply circuit being completed in one state of the controlling circuit, and there being provided a twostate switch, being closed in one state and open in the other state, connected to' the controlling circuit to change the state of the controlling circuit at each change of state of the switch, whereby in the primary winding the direction of current flow from the source is reversible by each change of state of the switch.

References Cited UNITED STATES PATENTS 3,018,413 1/1962 Neapolitakis 123148 X 3,229,162 1/1966 Loudon 3l5276 3,242,916 3/1966 Coufal 123148 3,252,168 5/1966 Robbins 123-148 MARK NEWMAN, Primary Examiner.

LAURENCE M. GOODRIDGE, Examiner. 

1. IN AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE, AN IGNITION COIL HAVING A PRIMARY WINDING AND A SECONDARY WINDING, A SOURCE OF UNI-DIRECTIONAL CURRENT, A FIRST SUPPLY CIRCUIT CONNECTING THE PRIMARY WINDING TO THE SOURCE TO PROVIDE FOR CURRENT FLOW IN ONE DIRECTION IN THE PRIMARY WINDING, A SECOND SUPPLY CIRCUIT CONNECTING THE PRIMARY WINDING TO THE SOURCE TO PROVIDE FOR CURRENT FLOW IN THE OPPOSITE DIRECTION IN THE PRIMARY WINDING, AN NPN TRANSISTOR IN THE FIRST SUPPLY CIRCUIT AND A PNP TRANSISTOR IN THE SECOND SUPPLY CIRCUIT, A TWO-STATE BIAS-POTENTIAL CONTROLLING CIRCUIT INTERCONNECTING THE SOURCE AND THE TRANSISTORS, AND A TWO-STATE SWITCH CONNECTED TO THE CONTROLLING CIRCUIT TO CHANGE THE STATE OF THE CONTROLLING CIRCUIT AT EACH CHANGE OF STATE OF THE SWITCH, THE SWITCH BEING CLOSED IN ONE STATE AND OPEN IN THE OTHER STATE, THE NPN TRANSISTOR BEING IN CONDUCTIVE CONDITION AND THE PNP TRANSISTOR BEING IN NON-CONDUCTIVE CONDITION IN ONE STATE OF THE CONTROLLING CIRCUIT AND THOSE CONDITIONS OF THE TRANSISTORS BEING REVERSED IN THE OTHER STATE OF THE CONTROLLING CIRCUIT, WHEREBY IN THE PRIMARY WINDING THE DIRECTION OF CURRENT FLOW FROM THE SOURCE IS REVERSIBLE BY EACH CHANGE OF STATE OF THE SWITCH. 